Senate Judiciary ranking member Chuck Grassley (R-Iowa) called for Assistant Attorney General Lanny Breuer to resign or be fired today on the Senate floor, the latest development in the fallout over the Operation Fast and Furious gun-trafficking case.

“I’ve done oversight for many years, and in all that time, I don’t ever remember coming across a government official who so blatantly placed sparing agencies embarrassment over protecting the lives of citizens,” Grassley said.

Documents released last week show Breuer’s office played a key role in the drafting of a Feb. 4 letter to Grassley that Attorney General Eric Holder has since admitted contained false information about Fast and Furious.

In the letter, Assistant Attorney General Ronald Weich broadly denied that ATF officials had allowed assault weapons to “walk,” which meant ending surveillance on weapons suspected to be en route to Mexican drug cartels. “ATF makes every effort to interdict weapons that have been purchased illegally and prevent their transportation to Mexico,” Weich wrote.

Breuer conceded on Oct. 31 that he knew federal officials allowed guns to fall into the possession of Mexican drug cartels 10 months before the department denied in February that such an investigative strategy was used.

“This was a shocking revelation,” Grassley said today. “The controversy about gun walking in Fast and Furious had been escalating steadily for 10 months. The Justice Department had publicly denied to Congress that ATF would ever walk guns. Yet, the head of the Criminal Division, Mr. Breuer, knew otherwise and said nothing.”

Breuer’s knowledge of the tactic stemmed from Operation Wide Receiver, a similar, smaller-scale weapons-smuggling investigation that began during President George W. Bush’s administration.

Justice Department spokeswoman Tracy Schmaler said in a statement that Breuer has “acknowledged his mistake in not making — and therefore not alerting Department leadership to — a connection between the allegations made about” Fast and Furious and the “unacceptable tactics used years earlier” in Wide Receiver. Schmaler added that Holder “continues to have confidence” in Breuer’s “ability to lead the Criminal Division.”

Breuer said in October that it was a “mistake” not to alert higher-ranking officials when the information about gun walking in Fast and Furious “became public,” given his knowledge about Wide Receiver.

Emails show Breuer received versions of the Feb. 4 letter on four occasions via email. Breuer forwarded the emails to a personal account but told Congressional investigators in a written statement last week that he “cannot say for sure” whether he viewed the drafts.

He also asked Jason Weinstein, his deputy, to “let me know what’s happening with this” in a Feb. 1 email asking for an update, among other interactions on the topic.

Grassley questioned whether Breuer’s claim to not remember whether he read the letters was credible.

“It just isn’t credible that someone like Mr. Breuer would forget about his involvement in a matter like this,” he said.

In a Feb. 1 letter, Weinstein told William Hoover, then the deputy director of the Bureau of Alcohol, Tobacco, Firearms and Explosives who has since been reassigned, that Breuer had encouraged him to intervene on the issue.

“As you know, Lanny is one of ATF’s biggest supporters — he has encouraged me to do whatever we can to help. Just wanted to pass that along,” Weinstein wrote.

Weinstein, like Breuer, was familiar with Wide Receiver, bringing the matter to Breuer’s attention in April 2010, according to documents released in October. Weinstein told colleagues then that ATF should be “embarrassed that they let this many guns walk” in Wide Receiver.

But when asked by Grassley whether ATF was allowing guns to walk in late January, Weinstein; Dennis Burke, then a U.S. attorney who has since resigned; and Hoover all pushed the Justice Department’s Office of Legislative Affairs to broadly deny the agency was.

According to the documents released last week, Burke was vehement on the subject, repeatedly urging Faith Burton — a Justice Department official who drafted an early version of the February letter — and other officials to strengthen the letter’s denial, which in some versions called allegations about gun walking “categorical[ly]” false.

“What is so offensive about this whole project is that Grassley’s staff, acting as willing stooges for the Gun Lobby, have attempted to distract from the incredible success in dismantling [southwest border] gun trafficking operations ... but, instead, lobbing this reckless despicable accusation that ATF is complicit in the murder of a fellow federal law enforcement officer,” he wrote in a Feb. 4 email.

“Well said Dennis. Thank you!” Hoover replied.

House Oversight and Government Reform Chairman Darrell Issa suggested in an interview with Roll Call today that Burke knew guns were walking when he urged Justice Department officials to deny it.

“How did he think he could get away with saying what he said with what he did know?” the California Republican asked.

Congressional investigators will interview Burke on Dec. 13 for the second time. Burke was interviewed Aug. 18, but “he became ill and asked that we pause. And it’s been quite a pause,” Issa said.

“Let me assure you, in light of new documents, our questions will be expanded,” he added.

When asked for comment, Oversight and Government Reform ranking member Elijah Cummings (D-Md.) said, “I don’t have enough information.”

Like Breuer, Weinstein and Burke, Hoover faces questions about what he knew and when.

Based on a phone conversation with Hoover, Burton took notes that read, “ATF doesn’t let guns walk,” as well as language similar to the letter’s “every effort” sentence.

In an interview with Congressional investigators July 21, Hoover struggled to explain how he could have been ignorant about Fast and Furious when he had intervened on Wide Receiver, according to a transcript of the interview obtained by Roll Call.

In 2007, Hoover came down hard on an ATF office in Phoenix where both Wide Receiver and Fast and Furious originated, expressing concern that guns had been allowed to walk in Wide Receiver.

“I’m pretty confident they weren’t real happy with me, because I was asking them to provide me a ton of information,” Hoover told investigators.

But how could the same office launch a wider, more aggressive use of the same tactic in Fast and Furious contrary to his instructions?

“That would be a life’s lesson for Bill Newell: Make sure you have these things in place as you move forward,” Hoover said, appearing to lay blame on Newell, who headed ATF’s Phoenix office.

“But he had the life’s lesson back in ’07?” the Congressional investigator asked.